The Glock 21 is a full size high capacity auto in .45 ACP. I think the high caps hold thirteen, used to have one but traded it for the Glock 22 .40 to shoot in IDPA. The high caps also sell for anywhere from 75 to 100 bones a piece.

The Glock 21 Hi Cap does hold 13 rounds, but are getting expensive. Probably $120 for a third generation mag. You can also get a +2 mag extender, giving you 15 rounds total, from places like www.glockmeister.com